Every
year I get an early start on the season by growing dozens of plants
from seed for transplanting into the garden. Raised under fluorescent
lighting (please see FLUORESCENT
PLANT LIGHTING
for my system,) they let me get a two-month head start. Growing the
best plants requires that the best potting mix be used to ensure
maximum germination and the fastest, healthiest growth. To determine
which potting mix works the best I compared a high-end professional
mix from Peaceful Valley Farm Supply against four commonly available brands.

For
each potting soil I filled a 1-quart plastic pot level to the top
with each mix and after placing it in a larger container, soaked it
from the bottom with warm water until all of the mix was saturated.
It was left in the water for 10 minutes to ensure every fiber had
been hydrated then moved to a draining rack for excess water to drain out.

Peaceful
Valley Farm Supply potting soil
is extremely coarse, contains a very high amount of large irregular
pieces of perlite and contains many pieces of what looks like long
sections of fine plant roots. It scooped and wetted easily and did
not shrink very much after its initial soaking.

Jiffy
Mix This mixture of peat moss and
very fine perlite wetted very easily but shrank 30-percent after its
initial soak. I had to add more mix and resoak it to end up with the
same amount of soil as the other mixes.

Miracle
Grow This mix looked and behaved
like pure peat moss. Even though it felt damp out of the bag it
aggressively repelled water. I had to repeatedly stir it into the
water to get it to hydrate. Extremely messy and frustrating to use.
After draining it shrank even more than Jiffy Mix.

Hyponex
By far the heaviest of the mixes, either dry or wet. It's a very dark
mix containing both medium and fine particles with a very few bits of
tiny perlite. The top of the mix in the bag was damp and wetted
easily. The bottom was drier and repelled water a little. An
extremely rich-looking mix when wet. Very little shrinkage.

SuperSoil
A medium coarse mix that is a delight to use. It scoops very easily
and wets the best of all the potting soils compared. Wet or dry it is
the lightest of the mixes, which would be advantageous if it's going
to be used in a very large pot that has to be moved around. It's
extremely fast and easy to bottom water and drains quickly. Very
little shrinkage. Although not quite as rich looking as the Hyponex
potting soil, it still looks like it has an outstanding texture for
seedling emergence and plant growth.

Water
retention:

From left to right:Peaceful Valley, Jiffy Mix,
Miracle Grow, Hyponex, and SuperSoil

The
picture above shows each of the potting mixes after they had drained
for 12 hours. The Hyponex, fourth from the left, was by far the
heaviest and as can be seen retained the most water. Jiffy Mix and
Miracle grow appeared to retain equal amounts of water but Miracle
Grow's slightly greater weight indicates that it won the tie. The
lightest mix was Supersoil, suggesting it might require more frequent watering.

While
high water retention may seem to be a good thing, plant roots also
require oxygen to grow properly. Jiffy Mix, Miracle Grow and Hyponex
ended up being so dense that this might be a problem.

Potting
soil comparison methodology:

Six
pots were filled with each brand of potting soil, soaked for 10
minutes to thoroughly hydrate them and then planted with a known
number of tomato or muskmelon seeds. They were then covered with
transparent plastic and placed in an artificially lighted and heated
growing chamber until the seeds germinated, at which time the plastic
was removed. All together 30 pots planted with 54 tomato and 15
muskmelon seeds distributed equally among the five brands of potting
soil were prepared.

Each
pot was watered once a week with a solution containing an organic
fertilizer (Omega 6-6-6 by Peaceful Valley Farm Supply) and a B-1,
boron, iron, manganese, and zinc supplement.

The
potting soil brands were rotated through every position in the
growing chamber to eliminate the chance that one brand might
accidentally be located an a location that receives more light or
fresh air.

Results:

Germination:

The
following picture was taken after all the seeds that were gowing to
germinate had germinated:

From left to right there are 6
pots each of Peaceful Valley Farm Supply,Jiffy Mix, Miracle Grow Organic,
Hyponex, and Supersoil potting soil.

Supersoil
provided the fastest germination with plants emerging 12 hours ahead
of Jiffy Mix, Hyponex and Peaceful Valley Farm Supply potting soils.
Miracle Grow Organic potting soil was the slowest, a full day behind
the middle group and a day and a half behind Supersoil Potting soil.

Hyponex
and Supersoil had the highest germination rates at 87-percent each.
Peaceful Valley came in next at 83-percent, Jiffy Mix was fourth at
75-percent and Miracle Grow's Organic potting soil came in dead last
at only 67-percent.

At
this stage the plants are so young that they still haven't sprouted
their first set of true leaves. As such I had assumed there wouldn't
be any significant differences in how they were growing. I was wrong.

While
looking for which potting soil planted with muskmelons showed the
best root development I was amazed that while none of the others
showed a single root growing against the side of its container after
the first week, the Peaceful Valley potting soil clearly showed an
aggressive network of roots on all four sides of its pot. I attribute
this to Peaceful Valley inoculating their potting soil with mycorrhizae
fungi,
which are well known to promote vigorous root growth.

Such
rampant root development is good because it creates a much more
substantial root base to nourish the plant. One extremely minor
drawback is it that this rapid root growth could lead to the plant
quickly becoming root bound. I don't consider this a serious issue
because simply using a large pot takes care of it. I'd happily trade
purchasing a little more of this top-quality potting soil and larger
pots for plants with big, healthy roots that are many times the size
of the next best option.

Watering:

I
prefer watering potted plants by placing them in a container that's
slightly larger than them and filling it with water so that it seeps
into the potting soil very gently from the bottom. This prevents the
formation of dry pockets, which can occur with top watering, disturbs
the roots the least and avoids digging holes in the surface by water
pouring in. For this reason I rate potting soils that quickly pull up
water from the bottom higher than those that are so dense that they
inhibit the inflow of water. In this regard Peaceful Valley Farm
Supply's potting soil is the best with Supersoil coming in a close
second. Hyponex was third and barely satisfactory. The extremely high
peat component of both Jiffy Mix and Miracle Grow Organic potting
soils render them so dense the bottom watering is a painfully slow process.

Growth
Rates:

After
19 days I compared first how the melons grew, turning the pot in
each case so that the melons displayed in the same orientation to
make comparisons easier.

From
left to right: Supersoil, Peaceful Valley, Jiffy Mix, Hyponex and
Miracle Grow Organic potting soil. Supersoil is the clear winner. (I
soaked the soil off the roots of the Supersoil and Peaceful Valley
potting soils to compare root development. Although the Peaceful
Valley soil was larger at the beginning, after 19 days the roots
growing in Supersoil were a full 10-percent larger.)

Next
I compared how the potting soils did in growing tomatoes. The
variety in each row, top to bottom, was: Burpee's Big Beef, Sun Gold,
a second row of Sun Gold, and finally Burpee's Supertasty.

The
potting soils from left to right are Supersoil, Peaceful Valley,
Miracle Grow Organic, Hyponex, and finally Jiffy Mix. (The missing
pot in the second row of Sun Gold tomatoes in the Miracle Grow column
was because none of the seeds in that pot germinated.)

The
results here are not as obvious as with the melons. Although in this
image the plants in the Peaceful Valley soil (second column from the
left) look slightly larger than those in Supersoil, in person the
plants grown in Supersoil were much more robust and had a healthier,
darker shade of green to their leaves. If I were choosing which
transplants to buy I'd take those growing in Supersoil.

Conclusions:

Supersoil's
high germination rate and superior growth in both melon and tomato
seedlings make it the preferred choice of the potting soils tested.
When the additional factors of ease of handling, easy watering, fast
drainage and low cost are also considered, it is the clear winner.

Peaceful
Valley Farm Supply's potting soil came in a close second. But, the
fact that it's four times the price of Supersoil after adding in the
cost of shipping and not conveniently available makes it much less
desirable. Another downside is that it contained weed seeds that
germinated in the sample I tested. This was an annoyance that could
be a serious problem for someone whose desired seedlings looked like
the germinating weeds. How would he or she know which to remove?

They
are many dozens of other potting mixes on the market that I wasn't
able to test so this experiment can't be considered definitive. But,
it strongly suggests that Supersoil potting soil is a superior
product capable satisfying anyone's gardening needs. It's certainly
the brand I'll be using in my garden from now on.

PRODUCT
WARNING!!!

Gardener
and Bloome Potting
Soil

The
year before the above comparison I purchased four bags of Gardener
and Bloome's Rose Potting soil and used it to plant 77 pots with
zinnia, tomato, melon, Canterbury bell and salvia seeds. The results
were a complete disaster. Although I followed my regular routine for
growing seedlings, a routine that's worked flawlessly for over 20
years, with this brand of potting soil I only got a 20-percent
germination rate, the few plants that came up grew poorly, exhibited
many disease symptoms and 30-percent of them died. Upon testing the
soil I discovered that in spite of the package advertisements stating
that the soil contained a wide spectrum of organic amendments such as
bat guano, worm castings, kelp meal, alfalfa meal and so forth, the
soil was completely lacking in nitrogen, potassium and phosphorous.
Even after adding extra fertilizer the plants grew poorly. I've used
many potting mixes over the years and this is clearly the worst.
Perhaps I got a bad few bags out of what may otherwise have been a a
good production run, but for myself I will never use this product again.

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